Concretized structural evolution supported assembly-controlled film-forming kinetics in slot-die coated organic photovoltaics

Bulk-heterojunction structured small-area organic solar cells are approaching 20% power conversion efficiency, but the blurred film-forming kinetics in the fabrication of large-area devices causes significant PCE loss and restrains the potential of commercialization. Such blurring came from insufficient knowledge of structural evolution during the film-forming process. Here, we concretize the evolution process with structures detailed to the submolecular level by comprehensive investigations of in-situ UV-vis spectroscopy, Atomic Force Microscope, Grazing Incident Wide Angle X-ray Scattering, and molecular dynamic simulation. With such hierarchical structural knowledge, assembly-controlled film-forming kinetics is proposed to explain the whole picture. Such assembly is determined by molecule configuration and can be tuned via external conditions. Understanding this kinetics will contribute to screening large-area device fabrication conditions, and the detailed structural knowledge could inspire the future design of novel photovoltaic materials that are intrinsically excellent in large-area device fabrications.

1.The study presented in this paper provides a detailed investigation of morphology evolution.However, the relationship between this morphological difference and device performance could be further explored.For instance, it is observed that devices prepared by slot-die coating exhibit generally lower Voc compared to those prepared by spin coating.This raises the question of whether there exist other microstructures, beyond the dimer structures and morphologies discussed in the article, that are more favorable for enhancing OPV performance.The authors are suggested to provide same brief discussions on this topic.
2. A more detailed description of the in-situ measurement of the absorption spectra would be appreciated.Specifically, it would be beneficial if the authors could clarify whether the spectrum is measured in reflection mode or transmission mode.Furthermore, it is important for the authors to explain how the absorption spectrum is determined, whether it is calculated using the equation A=1-R, A=1-T, or A=1-R-T.Additionally, it would be helpful to specify whether the absorption spectrum is measured on devices or using organic blend films.
3. In this study, the authors summarize the structural formation process of active thin films containing acceptors with different side chains deposited via xylene.It would be beneficial for the authors to clarify whether the observed patterns of structural formation can also be applicable to blended films deposited using other solvents.4. A higher coating temperature appears to improve device performance.I wonder if the authors could further increase the coating temperature to over 100°C to investigate whether significantly altering the coating conditions can lead to a change in the growth mode of the blended active layer.
5. It appears that the coating temperature affects both Jsc and FF of the solar cells based on Y6 and L8-BO, but has minimal impact on the FF of the solar cell based on N3, despite significant changes in the morphology of the active layer.It would be helpful if the authors could provide an explanation for this observation.
6.It is recommended to provide JV curves and EQE spectra for all the solar cells investigated in this study.This would enable a better understanding of the role played by the acceptor side chain in determining the morphology and performance of slot-die coated solar cells.
7. In the first paragraph of the results section, the statement "Later, AFM and GIWAXS results indicate large morphology differences in tens of Angstroms and larger scales" is unclear and requires rephrasing.
It is unclear what is meant by "morphology differences in tens of Angstroms."8.In the second paragraph of the results section, it is mentioned that "PCEs of 1 cm2 devices made from PM6/Y6 analogues are dramatically different in numbers and temperature dependency".The temperature dependency mentioned here needs to be further clarified.It should be specified that this temperature refers to the substrate temperature rather than the temperature of the slot-die head or any post-annealing temperature.9.In the first paragraph of the discussion section, it is stated that "our capability in the manipulation of nanoscale morphology much stronger than before, such as targeted induction or inhibition of molecular assembly either by intentional molecular design or selective addition of certain additives."The authors should provide further clarification on how the results of this study contribute to the improvement of the selection rule for additives.
Reviewer #3 (Remarks to the Author): In this manuscript, Zhang et al. did a fascinating work by incorporating multiple experimental procedures and simulations to unveil the critical assembly structure and film-forming kinetics of famous Y6 analogues in slot-die-coated large-area organic photovoltaics.Each of the used characterization techniques was broadly applied to the topic of organic photovoltaics, but the authors made an inspiring elucidation on how to combine them to yield more profound insights.Among these, the proposition of a star-shaped trimer is the most fascinating part of the work, where authors did their best to concretize the assembly structure, via both in-situ spectroscopy and GIWAXS characterization.The evidence presented in this manuscript is convincing enough to support the proposed structure and the following kinetic model.I recommend the manuscript be published in Nature Communications after minor revisions.Several concerns that could be addressed are listed as follows: 1.The presented UV-vis spectrums in Fig. 2 have significant differences compared with each other.But since the authors only showed one in-situ UV-vis spectrum for each condition (including that in supporting information), this raises the concern of repeatability of the observed phenomenon.It would be much better if the author could provide extra information on the repeatability of UV-Vis spectroscopy.
2.The authors mentioned the formation of nanocrystals and their size dependence on coating temperature.But no other experimental evidence except for the baseline shift in UV-vis spectroscopy is provided.Further evidence is highly desirable if the authors would like to make this claim.
3.The AFM image of PM6 in Fig. 3a is unprecedented in previous reports.Authors should perform the AFM characterization again to further investigate the origin of such a distinguished branch-like structure.Also, authors should add a color bar to the AFM images.
4.In Supplementary Note 3 and Fig. S11, authors brilliantly designed feature vectors for automated packing analysis of molecular dynamics trajectory.Such a tool is critical to the discovery of star-shaped trimers and other assembly forms from a large quantity of molecular dynamic trajectories.However, the definition and the calculation method of the principal axis seem to be missing from the supplementary note.The authors should further elucidate the procedure to calculate the principal axis, as well as the generation of mentioned feature vectors.
5.The analytical method used in the manuscript could be inspiring to the community.Moreover, the ML model used to automatically classify the packing motif in a molecular dynamics trajectory would be valuable in many more scenarios.We here suggest authors publicize the model and the generated dataset for further applications.

Response to the comments of reviewers
We would like to thank the referees for spending time on this paper and providing invaluable comments which substantially helped improve the quality of the paper.The manuscript has been revised according to the comments point-by-point.

Reviewer #1 (Remarks to the Author):
The manuscript concretized the structural evolution during film-forming kinetics of slot-die coating on a sub-molecular level by combing in-situ UV-vis spectroscopy, AFM, GIWAXS, and molecular dynamics simulation.It is crucial that combining various characterization techniques and simulation is proven effective in answering the complex questions of the structuralperformance relationship in the field of organic photovoltaics.The proposed assemblycontrolled film-forming kinetics would contribute to screening large-area device fabrication conditions and inspire the future design of novel photovoltaic materials.Thus, I support the publication of this work in Nature Communications.Before publishing the manuscript, the comments below should be addressed.

Response to comment:
We are grateful to the reviewer for the positive comments on our work.
1.In Fig. 2e, the lower slope of the purple line means that the PM6:N3 blend film has obvious tailing at the edge of the final state absorption.Does this tailing mean that the N3 stacking is more disordered?
Response: We generally agree with the claim proposed by the reviewer.The absorption of an ordered stacking will be more unified and centralized, reducing the FWHM of the observed peak.
However, if the packing is more disordered, the conjugation length in a film will vary to a larger extent than the orderly stacked film, creating a large variance in the transition energy of molecular orbital and thus a broader absorption peak.In our reported case, the obviously smaller slope of PM6:N3 blend came from a generally broader absorption peak.Thus, we could attribute the broadening of the absorption peak of PM6:N3 film to the more-closely-but-more-disordered stacking of N3 molecules.To address the concern, we have added the following brief discussion to our manuscript related to the discussion on page 6 as follows: "And the lower slope of the absorption edge, i.e., the purple line in Figure .2e, indicates a large variance in electron transition energy.The phenomenon suggests that PM6:N3 film may possess a more-closely-but-more-disordered stacking of acceptor molecules, further depicting its uniqueness compared with the other two Y6 analogues." 2. The use of λ(0-0) is inappropriate in describing the evolution of the spectrum.Per the authors' analysis, there are different absorbing types in different evolution pathways, i.e., the growing pattern and moving pattern.Multiple electron transitions are involved in the process, and thus it is blurring to assign λ(0-0) peak to a certain transition type.

Response:
We thank you for the careful reading and pointing out this misleading description.
We agree that ascribing the absorption peaks to the electron transition between the ground state and the lowest first excited state is inappropriate if the molecule structure behind the electron transition varies.Following your advice, we changed our description of the acceptor absorption peak from " 0−0 peak" to general "major absorption peak" to avoid the mislead.
3. In Fig. 2d-f, the intensity of the acceptor peak in PM6:N3 blend film is lower than that of the donor peak at the beginning, but there is no such phenomenon compared with the other two systems.Please give more explanation.

Response:
We thank you for addressing the abnormal phenomenon, which we failed to elucidate in detail.Multiple experiments have confirmed that the phenomenon, as shown in Figure R3, not being a result of an accident or mistake during our experiment procedures but connected to the attribute of the N3 molecule.The solution containing N3 molecules aggregates in an early stage of coating, prior to the observation window of our in-situ UV-vis spectroscopy.This reduces the concentration of N3 molecules in the solution, resulting in a lower peak position compared with the donor absorption peak.
To address the concern, we have added the following description and explanation to the end of the paragraph on page 7: "Over crystallization and change in the ratio of donor and acceptor also reflects on the initial state of the absorption spectrum.Compared with PM6:Y6 and PM6:L8-BO, the acceptor absorbance peak in the PM6:N3 blend is obviously lower.Such phenomenon can also be observed in spectrums coated under other temperatures." The following are some format issues.4. In Fig. S6, the scale bar is missing in AFM height graphs.Authors need to supplement.
Response: Thank you for carefully reading our supplementary information and pointing out the missing scalebar in our AFM images.After our inspection, we found that all our AFM images lack a scalebar, and thus we reprocessed all our AFM figures, including

Response to comment:
We are grateful to the reviewer for the positive comments on our work and high thoughts on the manuscript.
1.The study presented in this paper provides a detailed investigation of morphology evolution.
However, the relationship between this morphological difference and device performance could be further explored.For instance, it is observed that devices prepared by slot-die coating exhibit generally lower Voc compared to those prepared by spin coating.This raises the question of whether there exist other microstructures, beyond the dimer structures and morphologies discussed in the article, that are more favorable for enhancing OPV performance.The authors are suggested to provide same brief discussions on this topic.
Response: Thank you for addressing your concern.We noticed that previous reports have pointed out several factors that could affect the open circuit voltage of OPV devices.Donoracceptor spacing(Nat.Commun. 2021, 12, 6679), packing of acceptor molecules (Nat.Energy 2021, 6, 605-613 ), and even orientation of such packing will affect the   of devices (ACS Energy Lett. 2019, 4, 1057-1064).Furthermore, previous reports have also pointed out the close coupling between molecular vibration and non-radiative energy loss (Adv. Energy Mater. 2018, 8, 1702227), which could also affect device   .
To further understand the effect of molecule assembly and structure on the   in our system, we fabricated small-area devices using o-xylene with spin-coating technique and performed GIWAXS analysis to investigate the difference in microstructures.We summarize device performances of spin-coated small-area devices of PM6:Y6 analogues in Table S2 and GIWAXS characterization results of best cells in Fig. S15.We moved both supplementary tables to Table we could find the difference of   between small and large area devices.Moreover, the difference of Δ  , follows Δ ,3 > Δ ,8− > Δ ,6 .The Δ  between the best small-area device and large-area device fabricated with PM6:Y6 is only 0.027 V.While for L8-BO, such value raises toward 0.048 V, nearly twice compared with the former.However, GIWAXS results unveil significant differences in packing styles in N3-based films, moderate changes in L8-BO-based films, and little changes in Y6-based films.This could once again prove the strong correlation between the packing style of acceptors and   related loss in OPVs.
We have made following changes to the manuscript to address the concern: At the end of first paragraph in "In-situ UV-vis Spectrum of Slot-die Film-forming Process", staring on page 5: "When compared to small-area devices fabricated with spin-coating technique and o-xylene as a solvent, as shown in supplementary table 2, L8-BO achieves the best performance with both small and large area devices, Y6 obtain a mediocre result, and N3 excels in a small area but failed catastrophically in large area devices." At the end of the section "Multiscale structural analysis", starting on page 15: "The influence of such packing attributes on device performance is significant.In Figure S15 we analyzed and plotted GIWAXS results of the best spin-coated devices, which, qualitatively speaking, showed a heavy correlation between stacking change and performance deviance between small-area devices and large-area devices, where N3 systems showed the largest difference in packing styles and device performance, Y6 and L8-BO system changes less and thus retained most of their performance in small-area devices." At the end of "Assembly-controlled film forming kinetics" section, starting on page 23: "Following the analysis of our kinetics, it is now possible to discuss a bit more in detail about the performance deviation between small-area and large-area devices.Our kinetic model indicates an absorbing behavior of acceptor molecules onto the donor fibrils, which is generally bad for spacing between donor and acceptor and brings extra energy loss to the system.When focused on Y6 and L8-BO systems, we find out that loss in   when scaling up for L8-BO systems is nearly doubled compared with Y6 systems (0.048 V vs 0.027 V).We attribute such extra loss to the packing style shift of L8-BO systems.From Figure 3 and Figure S15 we could tell that L8-BO tends to assemble in a more relaxed formation when being slot-die coated (smaller q vector peaks dominate compared with spin-coated films), which could induce more coupling between charge transfer state and molecule vibronic states and thus brought excess energy loss." We've also added the fabrication conditions for small-area devices in the "method" section as follows: "The rigid small-area devices were fabricated by spin coating with an inverted device structure of glass/ITO/ZnO/active layer/MoOx/Ag.The patterned ITO glass was cleaned by sequential sonication in soap with deionized (DI) water, then in DI water, ethanol, and finally in isopropyl alcohol for 30 min each.After ultraviolet-ozone (Ultraviolet Ozone Cleaner, Jelight Company, USA) treatment for 15 min, the ZnO precursor was spin-coated on the ITO substrate at 4000 rpm to form an electron transporting layer ZnO.Then, the substrate was baked at 200 °C for 30 min.
The Donor and acceptor materials were dissolved in an o-xylene solvent with a total concentration of 16.7 mg/ml (D:A=1:1.2w/w).The active layers were spin-coated and postprocessed in an N2 glove box at room temperature following conditions listed in supplementary table 2. At a vacuum level of ≈1.0 × 10 -6 mbar, a thin layer (5 nm) of MoOx was deposited as the anode interlayer.Finally, a 160 nm of Ag was deposited onto the active layer to form a back electrode.Photovoltaic performance of small-area devices were measured in a N2-filled glovebox.Newport Thermal Oriel 91159 A solar simulator was used for J-V curves measurement under AM 1.5 G, and the light intensity was calibrated with Newport Oriel PN 91150 V Si-based solar cell.Typical cells have device areas of approximately 4 mm 2 .A mask with well-defined area (2.56 mm 2 ) was used in J-V characteristics as well.J-V measurement signals were recorded by Keithley 2400 source-measure unit."Fig. R1 2D GIWAXS image and in-plane peak splitting result of spin-coated PM6:Y6 analogue films.
Table R2.Performance of 1 cm 2 OPV devices coated under various temperature.
2. A more detailed description of the in-situ measurement of the absorption spectra would be appreciated.Specifically, it would be beneficial if the authors could clarify whether the spectrum is measured in reflection mode or transmission mode.Furthermore, it is important for the authors to explain how the absorption spectrum is determined, whether it is calculated using the equation A=1-R, A=1-T, or A=1-R-T.Additionally, it would be helpful to specify whether the absorption spectrum is measured on devices or using organic blend films.
Response: Thank you for addressing your concern.Here are the answers to your questions: 1) whether the spectrum is measured in reflection mode or transmission mode.
Our in-situ UV-vis spectroscopy was performed using transmission mode, with one fiber spectrometer obtaining the transmission signal.

2) how the absorption spectrum is determined, whether it is calculated using the equation A=1-R, A=1-T, or A=1-R-T.
The absorption spectrum is calculated using equation A=1-T, where A is absorption and T is the recorded transmittance signal.
3) it would be helpful to specify whether the absorption spectrum is measured on devices or using organic blend films.
The absorption spectrums were collected on organic blend films following the procedures in the method section.We also collected an in-situ spectrum of the active layer in the fabrication process of devices with the same fabrication process as organic blends.A comparison between in-situ spectrum of organic blend films and the active layer of devices is shown in Fig. R2.Qualitatively speaking, we consider no major deviation between the film formation kinetics in types of films.
To clarify the concerns in our manuscript, we made the following changes: On page 6, to the caption of Figure .1a:"Instrumental setup of slot-die integrated in-situ UVvis spectrometer which works on transmission mode".
On page 26, to the method section titled "Slot-die Process and In-situ UV-vis spectroscopy": "Transmission mode is used in the collection of in-situ spectroscopy signal." is added to the end of the first paragraph.

In this study, the authors summarize the structural formation process of active thin films containing acceptors with different side chains deposited via xylene. It would be beneficial for the authors to clarify whether the observed patterns of structural formation can also be applicable to blended films deposited using other solvents.
Response: Thank you for addressing your concern on the generality of our findings in the manuscript.We would like to try more solvent systems and further validate our kinetic model, but the experimental condition restricted our experiment with toxic halogen-containing solutions like chloroform and chlorobenzene, while PM6 seldom dissolves in tetrahydrofuran(THF).But still, we managed to analyze the film-forming process with UV-vis spectroscopy on films coated with toluene.
We summarized the findings put them in supplementary note 5.A brief discussion on results was added to the end of "Assembly-controlled film-forming kinetics" section as follows on page 23: "Moreover, we performed the same UV-vis spectroscopy analysis on the same systems with toluene as solvent.As shown in Figure S7 and Figure S8, it is astonishing to find that compared with o-xylene, toluene tends to facilitate aggregation of acceptors and thus leads to a higher portion of growing kinetics and crystallization.Details of the analysis can be found in Supplementary Note 5.The result is anticipated in our proposed kinetic model since toluene poses lower resistance packing with acceptor backbones compared with o-xylene, thus acting as a better lubricant and helping better in the assembly of acceptors."

A higher coating temperature appears to improve device performance. I wonder if the authors
could further increase the coating temperature to over 100°C to investigate whether significantly altering the coating conditions can lead to a change in the growth mode of the blended active layer.
Response: Thank you for suggesting on extending our experiment conditions.However, due to the thermal instability of the PET substrate, we could not further increase the coating temperature beyond 100°C.However, we managed to further investigate film-forming kinetics on glass substrates with a higher coating temperature of 115°C.Results of which are added to supplementary Figure 9. We've also tried coating under 130°C but the rapid evaporating solution had overrun our experimental setup, and we got no in-situ spectroscopy data for the rapidly changing phase.
From what we have collected, the higher coating temperature generally increases the growing portion of kinetics in all three blends.Especially for PM6:N3 system, the even-higher temperature further inhibited the over-crystallization, remedying baseline shift and deduction of acceptor absorption.Such a phenomenon is anticipated, as we have already discussed in supplementary note 4. All three blends coated here have already passed the critical point where solvent evaporation and molecule diffusion reach equilibrium.The faster solvent evaporation limits the diffusion of molecules and thus reduces the ability of chain formation, yielding a higher portion of grow kinetics in our model.
To have your concern settled, we have added a brief discussion at the end of our "Assemblycontrolled film-forming kinetics" section as follows on page 22: "We further tried coating blends on glass substrates with a substrate temperature of 115°C, the results of which are shown in Figure S9.After fitting with our grow-move two peak model the portion of growing peaks have all increased, which is in accordance with our kinetics, further strengthening the liability of our kinetic model."

It appears that the coating temperature affects both Jsc and FF of the solar cells based on Y6
and L8-BO, but has minimal impact on the FF of the solar cell based on N3, despite significant changes in the morphology of the active layer.It would be helpful if the authors could provide an explanation for this observation.
Response: Thank you for raising the concern.To answer in brief: a similar microstructure is the source of the near-constant fill factor of N3 system, while such one-phase morphology, according to previous research, is the source of its poor performance.
The morphology of PM6:N3 film, on a larger scale which could trigger observable Mie scattering effect, is significantly different from each other.However, on a scale of tens of nanometers, which can be proved by similar GIWAXS patterns and AFM images, the morphology of PM6:N3 films is similar.
In our kinetic model, similar morphology could result from a film where large quantities of N3 molecules had assembled and from large aggregates, while PM6 and remaining saturatedabsorbed N3 molecules form the actual film.In this state, we could actually consider the active layer to have only one phase, plus non-film forming N3 crystals.According to Ye et.al. (Nat. Mater. 2018, 17, 253-260), a film composed of one single phase usually comes with a low fill factor.

It is recommended to provide JV curves and EQE spectra for all the solar cells investigated in
this study.This would enable a better understanding of the role played by the acceptor side chain in determining the morphology and performance of slot-die coated solar cells.Response: Thank you for raising the concern on rephrasing the expression of our manuscript.

Response
We have modified the confusing sentence (on page 4) into: "Later, GIWAXS and AFM results suggest that the morphology of coated PM6/Y6 analogue films have significant differences on a scale from several molecules to aggregates with a few hundred nanometers." 8.In the second paragraph of the results section, it is mentioned that "PCEs of 1 cm 2 devices made from PM6/Y6 analogues are dramatically different in numbers and temperature dependency".The temperature dependency mentioned here needs to be further clarified.It should be specified that this temperature refers to the substrate temperature rather than the temperature of the slot-die head or any post-annealing temperature.
Response: Thank you for finding this blurring expression in our manuscript.To address the problem, we have modified our manuscript on page 5 as follows: "PCEs of 1 cm 2 devices made from PM6/Y6 analogues are dramatically different in numbers and dependency on the substrate temperature, as shown in the table and Figure S10" 9.In the first paragraph of the discussion section, it is stated that "our capability in the manipulation of nanoscale morphology much stronger than before, such as targeted induction or inhibition of molecular assembly either by intentional molecular design or selective addition of certain additives."The authors should provide further clarification on how the results of this study contribute to the improvement of the selection rule for additives.
Response: Thank you for requesting detailed discussion on the potential of our kinetic model and we appreciate your high value on our manuscript.To further clarify the selection rule of additives, we add the following discussion to the end of the first paragraph of the discussion section on page 24: "By understanding the primary assembly of acceptor molecules, additive molecules which target certain binding sites can be designed and synthesized to bind with acceptors, encouraging or discouraging certain types of assembly, and guiding the assembly toward another direction.For example, suppose a conjugated solid additive can be synthesized to target the core acceptor unit of Y6 and N3 molecule; such binding will reduce the formation of the star-shaped trimer, thus forcing the kinetics to move toward moving kinetic.Moreover, the host-guest strategy might also be applied to facilitate more favorable assembly patterns and multiscale morphology in the formation of active layers."

Reviewer #3 (Remarks to the Author):
In this manuscript, Zhang et al. did a fascinating work by incorporating multiple experimental procedures and simulations to unveil the critical assembly structure and film-forming kinetics of famous Y6 analogues in slot-die-coated large-area organic photovoltaics.Each of the used characterization techniques was broadly applied to the topic of organic photovoltaics, but the authors made an inspiring elucidation on how to combine them to yield more profound insights.Among these, the proposition of a star-shaped trimer is the most fascinating part of the work, where authors did their best to concretize the assembly structure, via both in-situ spectroscopy and GIWAXS characterization.The evidence presented in this manuscript is convincing enough to support the proposed structure and the following kinetic model.I recommend the manuscript be published in Nature Communications after minor revisions.Several concerns that could be addressed are listed as follows: Response to comment: We are grateful to the reviewer for the positive comments to our work and high thoughts on the manuscript.Especially the agreement on our experimental procedures developed in the manuscript.
1.The presented UV-vis spectrums in Fig. 2 have significant differences compared with each other.But since the authors only showed one in-situ UV-vis spectrum for each condition (including that in supporting information), this raises the concern of repeatability of the observed phenomenon.It would be much better if the author could provide extra information on the repeatability of UV-Vis spectroscopy.
Response: Thank you for raising your concern.We have to clarify that each experimental condition has been reproduced at least three times to avoid mistakes.Moreover, the statistical analysis in Fig. S17 is exactly the result of this repeated work.In the revised version of our manuscript, please find enclosed spreadsheets for all raw fitting results of our model used to draw Figure S18 in document S2 of supplementary information.To further prove the repeatability of our experiment, we put the result of the repeating experiment of Fig. 2a-c in Fig. R3 for your reference.Though the actual time between stage I and stage II varies from experiment to experiment, which is brought by the manual start of spectrum acquisition, the shape in the waterfall plot and the fitted result showed good repeatability.We believe such repeatability could satisfy the requirement of accuracy in our current manuscript.Response: Thank you for raising your concern.We have prepared pure PM6 films for new AFM imaging.It turned out that the branch-like structure could be the batch variance for PM6 since we could also observe a similar structure in the AFM image of blend films.But since a similar structure could not be reproduced, we would not conduct further analysis on such structure and replaced the original AFM image of PM6 film with new results.The discussion on AFM images in our manuscript on page 11 have also been modified as following:

3.The AFM image of PM6 in
"The morphology of pure PM6 film and three blend films was in great disagreement at first glance.Pure PM6 film exhibited a clear fibril feature, while in the Y6 blend's film, a spherical structure is observed with greater fluctuation in height.N3's blend showed a similar fibril structure compared with that of PM6 film while the L8-BO blend exhibited a flake-like structure."Also, thank you for pointing out the missing color bar problem when we process our AFM image, we thus redraw all our AFM images and added a color bar to each of them.
4.In Supplementary Note 3 and Fig. S11, authors brilliantly designed feature vectors for automated packing analysis of molecular dynamics trajectory.Such a tool is critical to the discovery of star-shaped trimers and other assembly forms from a large quantity of molecular dynamic trajectories.However, the definition and the calculation method of the principal axis seem to be missing from the supplementary note.The authors should further elucidate the procedure to calculate the principal axis, as well as the generation of mentioned feature vectors.
Response: Thank you for raising your concern.To further elucidate, we will answer your question in the following two topics:  Calculation procedure of principal axis for an acceptor molecule: 1) Determine the geometrical center for terminal groups of an acceptor molecule.In our case, terminal group refers to 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydro-1Hinden-1-ylidene)malononitrile units of Y6 analogues.
2) Set the line determined by the two geometrical centers as X-axis of the principal axis, and the midpoint of the line as principal center.
3) Determine Y axis.The Y axis would be the line in such a plane that: I. contains both geometrical centers, II. the summation of distance those backbone atoms to the plane reaches the minimum.Then, the Y axis will be the perpendicular line that intersect X axis at principal center.

Figure
photovoltaic (OPV) devices produced using the slot die coating method.Through the application of in situ spectroscopic analysis, the study revealed significant effects of the side-chain structure of acceptor materials on the film formation process of the active layer.The utilization of AFM and GIWAXS measurements provides clear insights into the formation of distinct microstructures in the active layers resulting from the use of acceptors with different side-chains.Additionally,

Fig. R2
Fig.R2 Comparison of in-situ UV-vis spectroscopy between organic blend and active layer of a

:
Thank you for raising the concern.Per your request, we have put all JV curves and EQE spectrums of the best cells for each coating condition in Figure S10.7. In the first paragraph of the results section, the statement "Later, AFM and GIWAXS results indicate large morphology differences in tens of Angstroms and larger scales" is unclear and requires rephrasing.It is unclear what is meant by "morphology differences in tens of Angstroms."

Fig. R3
Fig.R3 Result of repeated experiment of PM6:Y6 analogues with substrate temperature set at Fig.3a is unprecedented in previous reports.Authors should perform the AFM characterization again to further investigate the origin of such a distinguished branch-like structure.Also, authors should add a color bar to the AFM images.